I used to flinch and have made a lot of effort to stop, Like Critter said, have someone load a fired case in with the mix to make you aware of it. Doubling the ear pro helps, dry firing helps tons. I shoot a .204 Ruger and 7mm Rem mag. I like to start with the .204 then switch to the 7mm it takes the edge off from expecting the recoil. Having a good fitted stock helps. Keep your scope as far from your face as you can (depending on eye relief) relax and squeeze the trigger like you have no idea when its going to fire. DONT drink COFFEE or energy drinks before shooting... i wasted a trip to the range one day because of that. everytime my heart would beat i would shake the gun.
I don't flinch but still close my eyes when I fire. I havent figured out how to stop that.... been thinging about drinking a single beer to relax me before I shoot. (only at my personal range)